Dude... get real: WOMEN HAVE PERIODS.
Some women have short periods lasting 2-3 days, while others have periods lasting 8-9 days. Point is, at SOME point in you dating ANY woman, they will be on their period.
And, early on in the dating process, she's going to be VERY subconscious about sleeping with you when it's happening. You may be thinking "but it's no big deal, me want some now!"
SPOILER: it's a mood killer. I've slept with women who thought their period was done, or that it would be coming within a week, and then, in the middle of the festivities: SURPRISE!
Blood everywhere. Instand full stop. It's gross!
So, let's not just assume women are always "testing" us when they say this. They DO have periods. They STiLL want to feel like you'd want to spend time with them even if sex is temporarily off the table. More importantly, there's not enough of a pattern established of her blowing you off all the time for sex.